One of conventional DC/DC converters controls the amount of energy accumulated into a reactor and the amount of energy released from the reactor, using ON/OFF operation of a semiconductor switch, and performs voltage conversion from DC to DC. Since there is a problem that the reactor is large and heavy, there is known a technique of reducing voltage applied to the reactor by using charging and discharging of a capacitor, and reducing the inductance value required for the reactor, thereby reducing the size and the weight of the reactor.
One of such DC/DC converters includes a terminal group, a reactor, a switching element series circuit, a charge/discharge capacitor, a smoothing capacitor, and a control device, wherein the terminal group includes first to fourth terminals, the switching element series circuit has first to fourth switching elements connected in series, the connection point of the second and third switching elements is connected to the first terminal via the reactor, a side of the first switching element opposite to its connection point with the second switching element is connected to the second terminal, the charge/discharge capacitor is connected between the connection point of the first and second switching elements and the connection point of the third and fourth switching elements, the smoothing capacitor is connected in parallel to the switching element series circuit, the switching element series circuit is connected to the third and fourth terminals, the first and second terminals are set to be on a low-voltage side, the third and fourth terminals are set to be on a high-voltage side, and DC voltage conversion is performed between the low-voltage side and the high-voltage side.
The control device includes first calculation means, second calculation means, and open/close control means. The first calculation means calculates a first calculation value on the basis of difference voltage between a high-voltage-side voltage command value which is a voltage command value for the high-voltage side and a high-voltage-side voltage detection value which is a detected value of voltage on the high-voltage side, or difference voltage between a low-voltage-side voltage command value which is a voltage command value for the low-voltage side and a low-voltage-side voltage detection value which is a detected value of voltage on the low-voltage side. The second calculation means calculates a second calculation value on the basis of difference voltage between a voltage command value for the charge/discharge capacitor and a voltage detection value of the charge/discharge capacitor. The open/close control means calculates a current conduction rate on the basis of the first calculation value and the second calculation value, and controls open/close operations of the first to fourth switching elements on the basis of the current conduction rate (see, for example, Patent Document 1).